The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
In a series of previously issued and pending U.S. Patent documents several of the inventors named in connection with the present document have disclosed a family of electronic warfare radio receivers usable in obtaining militarily and otherwise useful information from an incoming microwave frequency radio signal including significant components of such receivers. Early in this sequence of patent documents the name xe2x80x9cmonobit receiverxe2x80x9d was used in referring to one embodiment of such a receiver and subsequently as a generic or family name for such receivers. Each of these receivers as preferably embodied has the attribute of employing a simplified multiplication in using the included Fourier transformation function in order that a simple and low cost realization of the receiver can be achieved.
In each of these simplified multiplications the Kernel function portion of the Fourier transformation is represented by a unit value, a magnitude of one or near one, in order to avoid the mechanization of a full fledged complex number multiplication algorithm. In fully implemented arrangements of such multiplications complex numbers representing an input signal are multiplied by a second set of complex numbers representing a Fourier transformation Kernel function. Generally the simplified multiplications have in our inventions in the past been accomplished by insuring the second set of complex numbers involve real and imaginary values of unity or near unity magnitude. As implied by the name xe2x80x9cmonobit receiverxe2x80x9d the earliest of these simplified Kernel function receivers employs a Kernel function approximation representable by a single binary bit of information while the later versions of the receiver and indeed the present invention involve Kernel function approximations requiring a greater number of bits, i.e., three or four, for their representation. These later receivers also observe the concept that some form of simplified and readily accomplished multiplication is required for practical reasons.
Fourier transformation Kernel functions of unit magnitude or substantially unit magnitude may therefore be used successfully to approximate a true Kernel function value and enable the realization of a Fourier transformation using only multiplication by unity or in essence no multiplication in the Fourier transformation computation algorithm. Kernel function realization in this manner,is first disclosed in a U.S. Patent of Tsui et al., numbered U.S. Pat. No. 5,917,737, a patent wherein Kernel function values are located on a circle of unit radius at angular locations of xcfx80/4, 3xcfx80/4, 5xcfx80/4 and 7xcfx80/4 radians i.e., at locations displaced by forty-five degrees from the real and imaginary axes of a coordinate axis plot. Actual coordinate axis locations of 1+j, 1xe2x88x92j, xe2x88x921+j and xe2x88x921+j are used for the Kernel functions disclosed in the U.S. Pat. No. 5,917,737 patent.
Our U.S. Pat. No. 5,793,323 relates to the U.S. Pat. No. 5,917,737 patent in that it discloses an integrated circuit chip arrangement for a monobit receiver employing the approximated Kernel function of the U.S. Pat. No. 5,917,737 patent. This patent also discloses several implementation compromises possible in applying the simplified Kernel function to receiver apparatus.
Our U.S. Pat. No. 6,448,921 also relates to the U.S. Pat. No. 5,917,737 patent in that it discloses the use of a monobit receiver in combination with several bandpass filters in order to increase the number of simultaneously processable signals and enhance the dynamic range capability of the overall system.
The invention of our U.S. patent application of Ser. No. 09/944,616, filed on Sep. 4, 2001, provides a straightforward approach to the enhancement of dynamic range in a monobit family receiver by increasing the number of Kernel function locations used in the Kernel function approximation from the four locations of the U.S. Pat. No. 5,917,737 patent and the U.S. Pat. No. 5,963,164 patent to eight locations. In the application of Ser. No. 09/944,616 Kernel function values located at the xcfx80/4, 3xcfx80/4, 5xcfx80/4 and 7xcfx80/4 radian locations are added to the Kernel function values at 0, xcfx80/2, xcfx80, and 3xcfx80/2 radians with the added four values being slightly increased in magnitude from true unit circle values and in fact having a magnitude of (2)xc2xd or 1.414. Some of these eight location Kernel function values depart slightly from unity magnitude, however, the overall results of the eight-location Kernel function appear favorable.
The invention of our U.S. patent application Ser. No. 10/008,476, filed on Dec. 10, 2001, also relates to the monobit receiver family in that it discloses a receiver from this family applied to a signal source locating or direction finding usage. The eight point Kernel function approximation of the type disclosed in the Ser. No. 09/944,616 application is also used in the invention of this Ser. No. 10/008,476 application.
Again a significant deficiency in the monobit receiver is that the instantaneous dynamic range achieved by the receiver is undesirably low. The instantaneous dynamic range relates to the receiver""s capability to detect two simultaneous signals of different amplitude. Because of the non-linear property of the approximated Kernel function in the original Tsui et al. U.S. Pat. No. 5,917,737 patent receiver, the instantaneous dynamic range of this receiver is limited to about 5 dB. Using a different Kernel function in the later tribit receiver of the Ser. No. 09/944,616 application can improve this instantaneous dynamic range to about 10 dB. However, one of the key concepts in the monobit and tribit receivers is that there is no multiplication accomplished in performing the fast Fourier transform of either receiver. Each of the patent documents identified in this BACKGROUND OF THE INVENTION discussion is hereby incorporated by reference herein.
The present patent document continues in this line of monobit and tribit, for example, receiver patents and provides additional insight into the unit magnitude and other approximated Kernel function realization. The present document also provides performance based comparative evaluations of receivers achieved with the Kernel function approximations disclosed in the identified prior patent documents and provides a current knowledge estimate of where the practical end points for this series of Fourier transformation Kernel function approximations and the associated receivers lies.
The present invention provides improved instantaneous dynamic range for the monobit and tribit receivers through Kernel function modification. The invention provides additional usable Kernel function values through a simplified form of multiplication involving the binary shift function.
It is therefore an object of the present invention to provide electronic warfare receivers of the monobit and tribit types having improved dynamic range characteristics.
It is another object of the invention to provide an additionally improved approximation of the Kernel function used in an electronic warfare receiver.
It is another object of the invention to provide an increased number of Kernel function values usable in an approximated Kernel function simplified multiplication electronic warfare receiver.
It is another object of the invention to provide an optimized approximated Kernel function electronic warfare radio receiver.
It is another object of the invention to provide a new set of approximated Kernel function values that are based on the binary shift multiplication algorithm.
It is another object of the invention to provide a sixteen-point approximated Kernel function usable with simplified forms of mathematical multiplication in an electronic warfare receiver.
It is another object of the invention to provide a sixteen-point simplified multiplication Kernel function quadbit electronic warfare receiver.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
These and other objects of the invention are achieved by the limited complexity method of analyzing input radio frequency signals, said method comprising the steps of:
generating an approximated Fourier transformation of successive segments of said input radio frequency signals;
said approximated Fourier transformation including individual Fourier series terms having real magnitude and imaginary magnitude coefficients generated by multiplication of input signal determined coefficients by selected approximated Fourier transformation Kernel function coefficients;
said selected approximated Fourier transformation Kernel function coefficients having magnitudes of unity and of two raised to an exponential power;
generating said individual Fourier series terms from said input signal determined coefficients and from said Fourier transformation Kernel function coefficients having real magnitude and imaginary magnitude coefficients of two raised to an exponential power using a bit shift multiplication algorithm; and
discriminating between spurious, approximated Fourier transformation-sourced and valid, input signal sourced components in a Fourier transformation output signal.